Camera with phased metalens

ABSTRACT

A camera includes a phased metalens positioned between an objective lens and an imager of the camera. The phased metalens is configured to adjust a focus plane of an image in a field of view of the camera in response to changes in an operating temperature of the camera. The phased metalens adjusts the focus plane for multiple frequencies or wavelengths light such that all light wave-fronts exiting the phased metalens arrive at the imager at a same time.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims priority to U.S.patent application Ser. No. 16/773,360, filed Jan. 27, 2020, the entiredisclosure of which is hereby incorporated by reference.

TECHNICAL FIELD OF DISCLOSURE

This disclosure generally relates to a camera.

BACKGROUND OF THE DISCLOSURE

Fixed focus cameras are typically aligned and focused at roomtemperature. These cameras may experience defocus, also known as achange in back focal length, over operating temperatures associated withvarious automotive applications due to thermal expansion and contractionof the camera.

SUMMARY OF THE DISCLOSURE

An example of a camera includes a phased metalens positioned between anobjective lens and an imager of the camera. The phased metalens isconfigured to adjust a focus plane of an image in a field of view of thecamera in response to changes in an operating temperature of the camera.

In an example having one or more features of the camera of the previousparagraph, the phased metalens is positioned within 1 mm of an imagerfocal plane.

In an example having one or more features of the camera of any of theprevious paragraphs, the phased metalens adjusts the focus plane formultiple frequencies or wavelengths of the light.

In an example having one or more features of the camera of any of theprevious paragraphs, the wavelengths range from 400 nanometers (400 nm)to 1600 nm.

In an example having one or more features of the camera of any of theprevious paragraphs, the phased metalens adjusts the focus plane over atemperature range of about 145 degrees Celsius.

In an example having one or more features of the camera of any of theprevious paragraphs, the phased metalens adjusts the focus plane overchanges in a focal length of about 16 microns (16 μm).

In an example having one or more features of the camera of any of theprevious paragraphs, the phased metalens comprises a plurality ofsub-wavelength structures positioned at predetermined coordinates acrossthe phased metalens.

In an example having one or more features of the camera of any of theprevious paragraphs, the plurality of sub-wavelength structures rangefrom two times to eight times smaller than a wavelength of the lighttransmitted through the phased metalens.

In an example having one or more features of the camera of any of theprevious paragraphs, the plurality of sub-wavelength structures aregrouped into a plurality of arrangements having unique phase profiles;the unique phase profiles configured to adjust a phase of the lighttransmitted through the plurality of arrangements.

In an example having one or more features of the camera of any of theprevious paragraphs, the unique phase profiles are based on thearrangement's respective radial distance from a center of the phasedmetalens.

In an example having one or more features of the camera of any of theprevious paragraphs, the unique phase profiles are based on an operatingtemperature of the camera.

In an example having one or more features of the camera of any of theprevious paragraphs, the plurality of arrangements define a plurality ofresolution units.

In an example having one or more features of the camera of any of theprevious paragraphs, the plurality of resolution units located at a sameradius from a center of the phased metalens have identical phaseprofiles.

In an example having one or more features of the camera of any of theprevious paragraphs, the plurality of resolution units located at adifferent radius from a center of the phased metalens have differentphase profiles.

In an example having one or more features of the camera of any of theprevious paragraphs, a size of one resolution unit is equal a size offour image pixels.

In an example having one or more features of the camera of any of theprevious paragraphs, each image pixel includes about 30 to 36sub-wavelength structures.

In an example having one or more features of the camera of any of theprevious paragraphs, each resolution unit includes about 120 to 144sub-wavelength structures.

In an example having one or more features of the camera of any of theprevious paragraphs, as the respective radial distance of the pluralityof resolution units increases from a center of the phased metalens, theunique phase profiles increase an amount of phase adjustment for a givenwavelength of light.

In an example having one or more features of the camera of any of theprevious paragraphs, as a radial distance of the plurality of resolutionunits increases from a center of the phased metalens, the unique phaseprofiles increase an amount of phase adjustment for decreasingwavelengths of the light.

In an example having one or more features of the camera of any of theprevious paragraphs, as a radial distance of the plurality of resolutionunits increases from a center of the phased metalens, the unique phaseprofiles increase an amount of phase adjustment for a given temperature.

In an example having one or more features of the camera of any of theprevious paragraphs, as a radial distance of the plurality of resolutionunits increases from a center of the phased metalens, the unique phaseprofiles increase an amount of phase adjustment for increasingtemperatures.

In an example having one or more features of the camera of any of theprevious paragraphs, all light wave-fronts exiting the phased metalensarrive at the imager at a same time.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example withreference to the accompanying drawings, in which:

FIG. 1 is an illustration of a cross sectional view of a camera, inaccordance with one example;

FIG. 2 illustrates an example of a focus characteristic of a phasedmetalens, in accordance with one example;

FIG. 3 is an illustration of the phased metalens viewed along an opticalaxis of the camera of FIG. 1 , in accordance with one example;

FIG. 4 is an illustration of the phased metalens viewed along an opticalaxis of the camera, in accordance with one example;

FIG. 5A is a plot of phase adjustment for blue light, in accordance withone example;

FIG. 5B is a plot of phase adjustment for green light, in accordancewith one example; and

FIG. 5C is a plot of phase adjustment for red light, in accordance withone example.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. In the following detaileddescription, numerous specific details are set forth in order to providea thorough understanding of the various described embodiments. However,it will be apparent to one of ordinary skill in the art that the variousdescribed embodiments may be practiced without these specific details.In other instances, well-known methods, procedures, components,circuits, and networks have not been described in detail so as not tounnecessarily obscure aspects of the embodiments.

FIG. 1 illustrates a cross sectional view of a camera 10 that includesan objective lens 12 and an imager 14. While the examples illustratedherein disclose the camera 10, it will be appreciated that thedisclosure also applies to other devices or sensors that senseelectromagnetic radiation, such as light detection and ranging (LiDAR)sensors. Multiple camera lenses (not shown) of varying geometries may beused in the camera 10, depending on the application requirements. Theimager 14 may be in electrical communication with a controller circuit(not shown) to process an image 16 of an object 18 in a field of view 20of the camera 10. In the example illustrated in FIG. 1 , a focal lengthof the camera 10 is fixed. That is, the camera 10 does not include amechanical or electrical focus adjustment device to refocus the image 16when a focus plane 22 of the camera 10 moves away from the imager 14(i.e., a defocus). In an example, thermal expansion and contraction ofthe camera 10, due to an operating temperature variation, may cause thecamera 10 to defocus. It will be understood that the focus plane 22 maymove in a positive direction (i.e., toward the objective lens 12) or anegative direction (i.e., toward the imager 14) along an optical axis 28of the camera 10, due to thermal expansion or thermal contraction of thecamera 10.

A typical camera used for advanced driver assistance systems (ADAS) maybe required to operate over a temperature range of −40° C. to +105° C.ADAS cameras are typically focused at 25° C. Depending on the materialsused in the camera body (not specifically shown), spacers, and lenses,this temperature range may result in a change in the focal length of thecamera 10 by as much as 16 microns (16 μm). ADAS cameras, that havefixed focus lenses with relatively large apertures and relatively lowf-stops, have a reduced depth of focus compared to more expensiveadjustable focus cameras. As a result, the thermal expansion of ADAScameras over the 145° C. temperature range will cause a significant andmeasurable (e.g., 25% to 50%) degradation in an image quality, which maynegatively affect the ADAS systems. Autonomous vehicle camerarequirements are continuing to drive toward smaller camera imager 14pixel sizes (e.g., 2 μm), higher density focal planes (e.g., 8 Megapixelarrays), and higher spatial frequency contrast image qualityrequirements (e.g., greater than 75 line pairs/mm). Consequently, theimage degradation over temperature for the larger format cameras will beproportionately higher and reduce object detection performance.

For a traditional fixed focus lens system, a change in back focal lengthof 15 μm-20 μm would require the same movement by the complete lenssystem, or could be accomplished by, a) introduction of a lens elementindex of refractive change (e.g., 6%-9% or representing a delta changeof 0.010-0.014), and/or b) lens element material thickness change (e.g.,20 μm-30 μm), and/or c) curvature change (e.g., 50 mm radius ofcurvature), and/or d) smaller contributions by combinations of theabove.

To address the defocus issue of the fixed focus camera 10, a phasedmetalens 24 is positioned between the objective lens 12 and the imager14 of the camera 10, as illustrated in FIG. 1 . The phased metalens 24is configured to adjust the focus plane 22 of the image 16 in the fieldof view 20 of the camera 10 in response to changes in the operatingtemperature of the camera 10. The phased metalens 24 accomplishes thisby shifting a phase of the incoming light rays via sub-wavelengthstructures 25, as will be described in more detail below. Thesesub-wavelength structures 25 (also referred to as nanostructures) may bedeposited on a relatively thin, generally planar, substrate of opticallytransparent material (e.g., optical glass), and may be formed ofmetamaterials with structural features that are capable of manipulatingthe light waves. In an example, the metamaterials are fabricated usingknown lithographic processes from compounds such as titanium dioxide,silicon nitride, boron nitride, molybdenum disulfide, or combinationsthereof. The metamaterials may be selected based on the wavelengths ofthe electromagnetic radiation being sensed. In an example, titaniumdioxide may be selected for light in the visible and near infraredspectrum. In an example, silicon nitride may be selected for light inthe visible spectrum. In an example, boron nitride may be selected forelectromagnetic radiation at wavelengths below the visible and nearinfrared spectrum (e.g., ultraviolet light). In an example, molybdenumdisulfide may be selected for electromagnetic radiation at wavelengthsin the near infrared spectrum.

FIG. 2 illustrates an example where the wave fronts of the light raysexiting from different regions of the phased metalens 24 reach theimager focal plane 26 at a same time (i.e., Δt=0, in phase). In anexample, the sub-wavelength structures 25 are fabricated on an exit sideof the substrate (i.e., the side facing the imager 14). In an example, across section of the sub-wavelength structures 25 normal to the incidentlight rays are rectangular. In another example, the cross section of thesub-wavelength structures 25 normal to the incident light rays arecircular. The phased metalens 24 is configured to shift the phase of theincoming light rays such that all light wave-fronts exiting the phasedmetalens 24 arrive at the imager 14 at a same time, resulting in goodfocus for all temperature conditions. That is, the phased metalens 24delays the light wave-fronts by differing amounts, depending on theposition of the sub-wavelength structures 25 on the phased metalens 24,such that all the light wave-fronts reaching the imager 14 are in-phase.The phased metalens 24 accomplishes this by achieving near diffractionlimited focusing over the incoming light wavelengths using preciselydefined nanoscale sub-wavelength resolution structures. In an example,the phase relationship for the phased metalens 24 is defined by thedesign wavelength, a sub-wavelength structure shape, and the phasedmetalens 24 focal length, using the known equation below,

${\varphi_{nf}( {x,y} )} = {\frac{2\pi}{\lambda_{d}}( {f - \sqrt{x^{2} + y^{2} + f^{2}}} )}$where λ_(d) is the design wavelength, f is the focal length for theconverging phased metalens 24 and x and y are the coordinates of thesub-wavelength structures 25 on the phased metalens 24. To account forthe focus variation across the operating temperature range, the phasedmetalens 24 includes the sub-wavelength structures 25 arranged in uniquephase profiles for the multiple focal lengths within the resolution unit30 that result from the temperature changes of the camera 10. That is,the phased metalens 24 includes multiple unique phase profiles designedfor multiple offsets of the focal length, so that as the focal length isoffset by the temperature change, the light rays exiting the phasedmetalens 24 will remain in phase.

FIG. 3 illustrates an example of a focus characteristic of the phasedmetalens 24 of FIG. 1 . The phased metalens 24 is configured to adjustthe focus plane 22 over the temperature range of about 145° C. and overthe associated changes in the focal length of about 16 μm. The phasedmetalens 24 adjusts the focus plane 22 for multiple frequencies orwavelengths of the light. In an example, the wavelengths range fromabout 400 nm to about 1600 nm (i.e., visible light to near infraredlight). In another example, the wavelengths range from about 400 nm toabout 700 nm (i.e., visible light only). In another example, thewavelengths range from about 700 nm to about 1600 nm (i.e., nearinfrared light only).

An aspect of the camera 10 is that the phased metalens 24 is placed inclose proximity to the imager 14. In an example, the phased metalens 24is positioned within 1 mm of an imager focal plane 26 (i.e., the imagingsurface of the imager 14). In an example, a thickness of the metalens 24is less than 1 mm, and preferably less than 25 μμm. This relatively thinstructure enables the metalens 24 to be positioned in the typicallynarrow space between the fixed focus objective lens 12 and the imagerfocal plane 26. This positioning enables a greater flexibility allowingfor the compensation of the thermal driven defocus while otherwise beingindependent of the existing fixed lens system.

FIG. 4 illustrates the phased metalens 24 viewed along an optical axis28 of the camera 10. The phased metalens 24 comprises a plurality ofsub-wavelength structures 25 (not shown) positioned at predeterminedcoordinates across the phased metalens 24. In an example, the pluralityof sub-wavelength structures 25 range from two times to eight timessmaller than the wavelength of the light transmitted through the phasedmetalens 24. In an example, the sub-wavelength structures 25 that shiftblue light (having wavelengths that range from 450 nm-485 nm) would havecross sectional dimensions normal to the incident light rays that rangefrom 0.050 μm to 0.150 μm. It will be recognized that light with longerwavelengths will require larger sub-wavelength structures 25 to causethe phase shift, and that light with shorter wavelengths will requiresmaller sub-wavelength structures 25 to cause the phase shift.

Referring back to FIG. 4 , the plurality of sub-wavelength structures 25are grouped into a plurality of arrangements having unique phaseprofiles that define a plurality resolution units 30 (RUs 30). That is,the plurality of sub-wavelength structures 25 are arranged into RUs 30that have unique phase profiles that delay the light transmitted throughthe RUs 30 by differing amounts of time. These unique phase profiles areconfigured to adjust the phase of the light transmitted through theplurality of RUs 30 based on the operating temperature of the camera 10,and also based on the RU's 30 respective radial distance from a centerof the phased metalens 24. FIG. 4 illustrates an example of two separateRUs 30 isolated from the plurality of RUs 30, having different phaseprofiles as denoted by “PHASE PROFILE 1” within the RU 30 positioned at“RADIUS 1”, and by “PHASE PROFILE 2” within the RU 30 positioned at“RADIUS 2”. In the example illustrated in FIG. 4 , the plurality RUs 30located at a same radius (e.g. RADIUS 1) from a center of the phasedmetalens 24 have identical phase profiles, and the plurality RUs 30located at a different radius (e.g. RADIUS 2) from the center of thephased metalens 24 have different phase profiles.

Referring again to FIG. 4 , in an example, a size of one RU 30 is equalthe size of four image pixels 32 of the imager 14. The maximum usefulimage resolution is limited to the Nyquist frequency, i.e., theresolution in pixel size scaled to the camera 10 imager focal plane 26pixel size. In this example, this is equivalent to the size of fourimage pixels 32. In an example, for the camera 10 with image pixels 32measuring 2 μm×2 μm in size, the limiting resolution is an area of 4μm×4 μm. Within this area, image information is sub-resolved or is notable to be reproduced or imaged, as such the area of 4 μm×4 μm is thelimiting dimension of the RU 30. Table 1 below illustrates an example ofa scale of various characteristics of a 3 mm×3 mm phased metalens 24.

TABLE 1 3 mm × 3 mm PHASED METALENS FEATURE SIZE RESOLUTION UNIT: 16 μm²(4 μm × 4 μm) IMAGE PIXEL AREA:  4 μm² (2 μm × 2 μm) SUB-WAVELENGTHSTRUCTURES: WIDTH 0.040 μm-0.100 μm LENGTH 0.150 μm-0.400 μm HEIGHT0.400 μm-0.600 μm ROTATION 0-2π RADIANS AREA 0.040 μm²-0.200 μm² NUMBEROF SUB-WAVELENGTH 30-36 STRUCTURES WITHIN AN IMAGE PIXEL: NUMBER OFSUB-WAVELENGTH 120-144 STRUCTURES WITHIN A RESOLUTION UNIT: NUMBER OFRUs: 562,500 NUMBER OF SUB-WAVELENGTH STRUCTURES: 67.5 MILLION-81.0MILLION

Referring to Table 1, in an example, each RU 30 includes about 120 to144 sub-wavelength structures 25. In this example, a focuscharacteristic encompassing a range of 11-12 discrete wavelengths with11-12 discrete temperature offsets may be included within a single RU30.

FIGS. 5A-5C are plots of radial distances of the sub-wavelengthstructures 25 from the center of the phased metalens 24 versus a phaseadjustment of the light. In this example, three colors (i.e.wavelengths) of visible light (blue, green, and red), at three operatingtemperatures (−40° C., 25° C., and +105° C.) are used to illustrate howthe phased metalens 24 adjusts the phase of the exiting light rays. Inthis example, as the respective radial distance of the plurality of RUs30 increases from the center of the phased metalens 24 towards theperiphery of the phased metalens 24, the unique phase profiles increasean amount of phase adjustment for a given wavelength of light. Referringto FIG. 5A (blue wavelength), the center of the phased metalens 24 isindicated at (0, 0) where the phase adjustment for the threetemperatures are nearly zero. As the sub-wavelength structures 25 aremoved away from the center of the metalens 24, the phase adjustmentincreases for the three temperatures indicated.

In the examples illustrated in FIGS. 5A-5C, as the radial distance ofthe plurality of RUs 30 increases from the center of the phased metalens24, the unique phase profiles increase an amount of phase adjustment fordecreasing wavelengths of the light. Comparing FIG. 5A, with FIG. 5B,and with FIG. 5C, the phase adjustment for the blue light in FIG. 5A isgreater than that for the green light of FIG. 5B, which is in turngreater than that for the red light of FIG. 5C. It will be understoodthat the wavelength of light increases from blue light to green light tored light.

In the examples illustrated in FIGS. 5A-5C, as the radial distance ofthe plurality of RUs 30 increases from the center of the phased metalens24, the unique phase profiles increase an amount of phase adjustment fora given operating temperature of the camera 10. Referring to FIGS.5A-5C, the plots of constant temperature show increasing phaseadjustment as the radial distance of the sub-wavelength structures 25increases from the center of the phased metalens 24.

In the examples illustrated in FIGS. 5A-5C, as the radial distance ofthe plurality of RUs 30 increases from the center of the phased metalens24, the unique phase profiles increase an amount of phase adjustment forincreasing operating temperatures of the camera 10. Referring again toFIGS. 5A-5C, as the temperature increases from −40° C. to 105° C., theamount of phase adjustment also increases.

While this invention has been described in terms of the preferredembodiments thereof, it is not intended to be so limited, but ratheronly to the extent set forth in the claims that follow. “One or more”includes a function being performed by one element, a function beingperformed by more than one element, e.g., in a distributed fashion,several functions being performed by one element, several functionsbeing performed by several elements, or any combination of the above. Itwill also be understood that, although the terms first, second, etc.are, in some instances, used herein to describe various elements, theseelements should not be limited by these terms. These terms are only usedto distinguish one element from another. For example, a first contactcould be termed a second contact, and, similarly, a second contact couldbe termed a first contact, without departing from the scope of thevarious described embodiments. The first contact and the second contactare both contacts, but they are not the same contact. The terminologyused in the description of the various described embodiments herein isfor the purpose of describing particular embodiments only and is notintended to be limiting. As used in the description of the variousdescribed embodiments and the appended claims, the singular forms “a”,“an” and “the” are intended to include the plural forms as well, unlessthe context clearly indicates otherwise. It will also be understood thatthe term “and/or” as used herein refers to and encompasses any and allpossible combinations of one or more of the associated listed items. Itwill be further understood that the terms “includes,” “including,”“comprises,” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. As used herein, the term“if” is, optionally, construed to mean “when” or “upon” or “in responseto determining” or “in response to detecting,” depending on the context.Similarly, the phrase “if it is determined” or “if [a stated conditionor event] is detected” is, optionally, construed to mean “upondetermining” or “in response to determining” or “upon detecting [thestated condition or event]” or “in response to detecting [the statedcondition or event],” depending on the context.

We claim:
 1. A camera, comprising: a phased metalens positioned betweenan objective lens and an imager of the camera, the phased metalenscomprising a plurality of sub-wavelength structures grouped into aplurality of arrangements at respective radial distances from a centerof the phased metalens, the arrangements configured to adjust phases oflight transmitted through the phased metalens based on the respectiveradial distances and colors of the light.
 2. The camera of claim 1,wherein the eater colors of the light transmitted through the phasedmetalens comprise wavelengths between 400 nm to 1600 nm.
 3. The cameraof claim 1, wherein the eerier colors of the light transmitted throughthe phased metalens comprise colors of visible light.
 4. The camera ofclaim 1, wherein the arrangements are configured to adjust the phasesfurther based on operating temperatures.
 5. The camera of claim 1,wherein the phased metalens is positioned within lmm of an imager focalplane.
 6. A system, the system comprising: an objective lens; an imagerconfigured to detect an image in a field of view of the system; and aphased metalens positioned between the objective lens and the imager,the phased metalens comprising a plurality of sub-wavelength structuresgrouped into a plurality of arrangements positioned at respective radialdistances from a center of the phased metalens, the arrangements havingrespective phase profiles configured to adjust phases of incoming lightbased on the respective radial distances and colors of the incominglight.
 7. The system of claim 6, wherein the sub-wavelength structuresrange from two times to eight times smaller than a the wavelengths ofthe incoming light.
 8. The system of claim 6, wherein plurality ofarrangements defines a plurality of resolution units.
 9. The system ofclaim 8, wherein a size of a resolution unit is based on a size of imagepixels of the imager.
 10. The system of claim 9, wherein each of theplurality of resolution units has a size equal to four image pixels. 11.The system of claim 8, wherein each of the plurality of resolution unitsincludes one hundred to one hundred forty-four sub-wavelengthstructures.
 12. A system, the system comprising: a phased metalenspositioned between an objective lens and an imager configured to detectimages in a field of view of a camera configured for a vehicle, thephased metalens comprising a plurality of sub-wavelength structuresgrouped into a plurality of arrangements at respective radial distancesfrom a center of the phased metalens, each arrangement of the pluralityof arrangements having a unique phase profile based on the radialdistance of the arrangement and a a color of light transmitted throughthe phased metalens.
 13. The system of claim 12, wherein, as the radialdistances of the plurality of arrangements increases, the unique phaseprofiles increase an amount of phase adjustment for a given color oflight.
 14. The system of claim 12, wherein each of the unique phaseprofiles increase an amount of phase adjustment for decreasingwavelengths of light.
 15. The system of claim 12, wherein each of theunique phase profiles increase an amount of phase adjustment forincreasing temperatures.
 16. The system of claim 12, wherein the phasedmetalens is configured to cause the light to arrive at the imager atapproximately the same.